We are using centrifugation to detach tissue culture cells from glass, plastic and other artificial substrata and in this way measuring the strength of their adhesions and comparing the adhesiveness of different cell types to a range of different substrata under different culture conditions. By interference reflection microscopy we are observing the location and movements of cellular adhesions, comparing the patterns of these adhesions formed by different cell types, counting the numbers of adhesions formed to artificial substrata of various degrees of adhesiveness and, combining this optical technique with micromanipulation determining whether all cell contacts are actually adhesions. By observing the initial spreading of trypsinized fibroblasts on gradients of substratum adhesiveness we are determining whether adhesion gradients control the direction of cellular locomotion by promoting spreading in the direction of increased adhesiveness or by promoting detachment in the direction of decreased adhesiveness. In addition, we are observing the locomotion of motile tissue cells through flexible gels, both in vitro and in vivo, as a way of observing, comparing and eventually measuring the tractional forces motile tissue cells exert. We are also using surface markers including adherent particles, ferritin, and fluorescent lectins to observe movements of the plasma membranes of motile tissue cells and relate these to the traction the cells exert during locomotion.